[PATCH][C++] Avoid PCH dependent mangling

[Richard Biener]

On Tue, 15 Sep 2015, Richard Biener wrote:

> On September 15, 2015 4:25:37 PM GMT+02:00, Jason Merrill <jason@redhat.com> wrote:
> >On 08/27/2015 09:36 AM, Richard Biener wrote:
> >>
> >> With the passes.c hunk in the patch below we FAIL assembly comparison
> >> of g++.dg/pch/system-[12].C because with PCH we have computed
> >> DECL_ASSEMBLER_NAME and thus appended DW_AT_linkage_name early during
> >> PCH generation while without PCH we compute it lazily and end up
> >> appending DW_AT_specification earlier.  Thus we have swapped dwarf
> >> attribute order and assembly comparison fails.
> >>
> >> Clearly this kind of "IL" changes dependent on whether we are writing
> >> a PCH file is going to cause differences down the food chain.
> >> (there is another case in instantiate_decl calling
> >add_pending_template
> >> dependent on pch_file)
> >>
> >> Now a simple solution is to simply not do that (mangle decls). 
> >Another
> >> would be to always mangle decls where we now do so conditional on
> >PCH.
> >> Another soulution is to declare we don't care about assembly
> >differences
> >> with/without using PCH and remove assembly comparison from the
> >> testsuite harness.
> >
> >Hmm, what if we walk through the symtab and mangle everything later, 
> >when we're about to write the PCH?  That should still get the benefit
> >of 
> >doing the mangling work only once, without changing the order of the 
> >attributes.
> 
> That might work if we can get at all relevant decls that way.  If not we 
> can populate a pointer-set from the function and walk that before 
> writing the PCH. I can do that if you prefer, I just didn't know if we 
> care about PCH performance enough to worry.

Ok, so the following fixes my pch.exp issues.  It drops note_decl_for_pch
in favor of mangling all globals before PCH write.

Bootstrap & regtest on x86_64-unknown-linux-gnu in progress, ok for trunk?

Thanks,
Richard.

2015-09-16  Richard Biener  <rguenther@suse.de>

	cp/
	* cp-tree.h (note_decl_for_pch): Remove.
	* class.c (build_clone): Do not call note_decl_for_pch.
	* semantics.c (finish_member_declaration): Likewise.
	(note_decl_for_pch): Remove.
	* decl2.c (c_parse_final_cleanups): Mangle all globals before
	writing the PCH.

Index: gcc/cp/class.c
===================================================================
*** gcc/cp/class.c	(revision 227779)
--- gcc/cp/class.c	(working copy)
*************** build_clone (tree fn, tree name)
*** 4691,4699 ****
    SET_DECL_RTL (clone, NULL);
    rest_of_decl_compilation (clone, /*top_level=*/1, at_eof);
  
-   if (pch_file)
-     note_decl_for_pch (clone);
- 
    return clone;
  }
  
--- 4691,4696 ----
Index: gcc/cp/semantics.c
===================================================================
*** gcc/cp/semantics.c	(revision 227779)
--- gcc/cp/semantics.c	(working copy)
*************** finish_member_declaration (tree decl)
*** 2951,2976 ****
        maybe_add_class_template_decl_list (current_class_type, decl,
  					  /*friend_p=*/0);
      }
- 
-   if (pch_file)
-     note_decl_for_pch (decl);
- }
- 
- /* DECL has been declared while we are building a PCH file.  Perform
-    actions that we might normally undertake lazily, but which can be
-    performed now so that they do not have to be performed in
-    translation units which include the PCH file.  */
- 
- void
- note_decl_for_pch (tree decl)
- {
-   gcc_assert (pch_file);
- 
-   /* There's a good chance that we'll have to mangle names at some
-      point, even if only for emission in debugging information.  */
-   if (VAR_OR_FUNCTION_DECL_P (decl)
-       && !processing_template_decl)
-     mangle_decl (decl);
  }
  
  /* Finish processing a complete template declaration.  The PARMS are
--- 2951,2956 ----
Index: gcc/cp/decl2.c
===================================================================
*** gcc/cp/decl2.c	(revision 227779)
--- gcc/cp/decl2.c	(working copy)
*************** c_parse_final_cleanups (void)
*** 4511,4516 ****
--- 4511,4522 ----
       In that case we do not want to do anything else.  */
    if (pch_file)
      {
+       /* Mangle all symbols at PCH creation time.  */
+       symtab_node *node;
+       FOR_EACH_SYMBOL (node)
+ 	if (! is_a <varpool_node *> (node)
+ 	    || ! DECL_HARD_REGISTER (node->decl))
+ 	  DECL_ASSEMBLER_NAME (node->decl);
        c_common_write_pch ();
        dump_tu ();
        return;
Index: gcc/cp/cp-tree.h
===================================================================
*** gcc/cp/cp-tree.h	(revision 227779)
--- gcc/cp/cp-tree.h	(working copy)
*************** extern tree finish_qualified_id_expr		(t
*** 6253,6259 ****
  						 bool, bool, tsubst_flags_t);
  extern void simplify_aggr_init_expr		(tree *);
  extern void finalize_nrv			(tree *, tree, tree);
- extern void note_decl_for_pch			(tree);
  extern tree omp_reduction_id			(enum tree_code, tree, tree);
  extern tree cp_remove_omp_priv_cleanup_stmt	(tree *, int *, void *);
  extern void cp_check_omp_declare_reduction	(tree);
--- 6253,6258 ----